The invention relates to a hydrodynamic bearing arrangement for a spindle motor used, for example, for actuation of hard disk drives.
Conventional spindle motors consist essentially of a stator, a rotor and at least one bearing system provided therebetween. The rotor, driven by an electric motor, is rotatably supported in relation to the stator by means of the bearing system. Both rolling bearings and hydrodynamic slide bearings can be used as bearing systems.
A hydrodynamic bearing system comprises a bearing sleeve and a shaft, which is provided in an axial borehole of the bearing sleeve. The shaft rotates freely in the bearing sleeve supported by a radial bearing formed by the shaft and the sleeve. A liquid or gas, used as lubricant between the bearing surfaces, is located in a bearing gap that separates moving bearing surfaces of the shaft and the sleeve. During operation, the lubricant, preferably oil, forms a portative lubricating film between the bearing surfaces. At least one of the reciprocally interacting bearing surfaces of the shaft and/or sleeve is provided with a grooved pattern which, as a result of the relative motion generated by rotation, exerts a pumping effect on the lubricant, thus generating the hydrodynamic pressure needed to provide bearing rigidity.
The specific advantages of hydrodynamic slide bearings over rolling bearings are greater operating precision, lack of sensitivity to impact stress (shock), and a smaller number of components. Since the sliding components do not come into contact with one another at the rated rotation speed, they operate with little wear and virtually without sound.
The amount of the lubricant filled into such a bearing system is critical to its reliable operation. A fill level that is only slightly lower than the correct fill level can significantly reduce the life of the bearing system, while an excess level can lead to subsequent leakage of the lubricant, thereby destroying the hard disk drive. A conventional bearing system is typically filled with a defined amount of lubricant following the assembly of the bearing system. In current bearing designs, it is not possible to check the fill level after the lubricant has been filled into the system to ensure that the fill level is correct.